Field of the Invention
The present invention relates to electrodeposition. In another aspect, the invention relates to electrodeposition employing polymers prepared by a new method in aqueous medium. More particularly, this invention relates to the polymerization of materials having CH.sub.2 .dbd.C&lt; moieties in the presence of a salt of an adduct of an unsaturated carboxylic acid or anhydride and polybutadiene.
Brief Description of the Prior Art
It is well known that adducts formed from relatively low molecular weight polybutadienes and maleic anhydride are capable of forming coatings that firmly adhere to metal. The adducts can be made water soluble by neutralization with an amine and used as vehicles for water-based coatings in applications such as electrodeposition. See, for example, U.S. Pat. No. 3,511,816 to Dickakian. Unfortunately, such materials are not particularly good for electrodeposition. As aqueous dispersions, they have poor throwpower; do not electrodeposit uniform coatings and the deposited coatings do not have particularly good corrosion resistance.
Besides the above prior art, U.S. Pat. No. 3,258,437 discloses polymers of butadiene prepared in the presence of aqueous medium containing the salt of an adduct of a drying oil and an unsaturated dicarboxylic acid or anhydride such as maleic anhydride. These polymers are prepared in the presence of a water-soluble salt-forming free radical polymerization catalyst; and, although they are excellent resinous vehicles for many coating applications such as dip or spray coating, they are unfortunately not suitable for use in electrodeposition. The salt-forming catalyst affects the conductivity of the bath, causing the polymers to coat out at high voltages which destroys film continuity.
The present invention provides polymers which are of relatively low viscosity and which form smooth continuous films on electrocoating.